How to pass arguments by reference to robot framework keywords? - pass-by-reference

Question

I have a keyword in robot framework; it takes an argument, performs some process on it and returns it after all:
My Keyword Name
[Arguments] ${arg}
# Some process on ${arg}
[Return] ${arg}
So it would be the usage:
${x} = My Keyword Name ${x}
Which implies that I gave the old value of ${x} to the keyword and it returned me the new value of it.
I want to make a call by reference on My Keyword Name, so I don't need to use an assignment for setting new value for ${x}. I have read the BuiltIn and UserGuide,
but there was no line about this subject. Can anyone help me on this?

Answer 1

If ${x} is a mutable type such as a list or dictionary, you can pass the object itself. If it represents a scalar value such as a string or int, you can't do what you want. Your only choice is to return the new value and re-assign it to the original variable.

Answer 2

It will work if you initialize the variable as
My Keyword Name
[Arguments] ${arg}
${arg} = Set Variable 56
[Return] ${arg}
Test
Log To Console \n\nin Test
${x} = Set Variable 0
${x} = My Keyword Name ${x}
Log To Console ${x}
Or
Can you explore whether you can make use of Set Global Variable or Set Test Variable?

Answer 3

I'd spent some time before i got the solution!
* Variables
${someVar} initial value
* Test Cases
[Check reference]
Set this \${someVar} new value
Should Be Equal ${someVar} new value
* Keywords
Set this
[Arguments] ${varName} ${value}
Set Test Variable ${varName} ${value}
The point is in the magic "\" char :)

Answer 4

It actually comes down to mutable/immutable variables in python, and how they are passed to functions.
Details here in this answer, but in RF context it boils down to - you can change lists and dictionaries, and not strings and numbers (int, float). Example:
A testcase
Log To Console \n
${var}= Create List member1
Log To Console ${var}
Mutate The List ${var}
Log To Console ${var}
*** Keywords ***
Mutate The List
[Arguments] ${lst}
Append To List ${lst} new one
The output when ran would be:
==============================================================================
A testcase
['member1']
['member1', 'new one']
| PASS |
, e.g. the variable defined in the case got changed by a keyword. The same can be done with dictionaries.
If you reassign the variable in the function though, it will not change; e.g. with a keyword like this:
Mutate The Dict
[Arguments] ${lst}
${lst}= Create List fsf
Append To List ${lst} bogus
, the original variable ${var} will not be changed.
Why so? In short, in python variables are just identifiers ("names") to memory addresses; when you assign ${lst} to a new list, the variable now points to a new address in the memory, and further interactions don't change the original one.

Answer 5

Welp I just ran into the same issue, as I was using a Run Keyword If statement in a For Loop. Knowing that if I used a keyword that returns a value, robot framework freaks out.
So I just thought of this as a potential solution. It'll use my example. It does have redundancy, but thats because you just have to in this case.
***Keywords***
| Increment | [Arguments] | ${var} |
| | ${var} | Evaluate | ${var} + 1 |
| | Set Test Variable | ${var} | ${var} |
Usage:
| Increment | ${idx} |
| Set Test Variable | ${idx} | ${var}
Now I'm not saying this is the best solution, but if you run into the scenario that you have to return a value to a variable with a keyword, and you're inside a "Run Keyword If", this should allow you to circumvent the issue. I don't really like it that much, but it gets the job done.